Union Station was the name of a transportation facility located on Earth. It was known for having a large volume of vehicles constantly arriving and departing.
In 2151 aboard Enterprise NX-01, Hoshi Sato claimed that the launch bay was like Union Station with shuttlecraft coming and going all the time. She did so after Sopek, aboard a Vulcan vessel, wanted to know where a shuttlepod was going. (ENT: "Shadows of P'Jem")